Method and apparatus for triggering transmission carrier selection in wireless communication system

ABSTRACT

A method performed by a user equipment (UE) in a wireless communication system, the method including: selecting to create a configured sidelink grant corresponding to transmissions of at least one media access control (MAC) protocol data unit (PDU); and triggering a transmission carrier selection procedure based on (i) data being available in a sidelink traffic channel (STCH) associated with one or more carriers, and (ii) there being no configured sidelink grant on any carrier, among the one or more carriers, that is allowed for the STCH.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/406,599, filed on May 8, 2019, which claims the benefit pursuant to35 U.S.C. § 119 (e) of U.S. Provisional Application No. 62/668,772,filed on May 8, 2018, the contents of which are all hereby incorporatedby reference herein in their entirety.

TECHNICAL FIELD

The present disclosure generally relates to wireless communications.

BACKGROUND

Wireless communication systems generally aim to reduce costs for usersand providers, improve service quality, and expand and improve coverageand system capacity. To achieve these goals, in some scenarios, wirelesscommunication systems are designed to reduced cost per bit, increasedservice availability, flexible use of a frequency band, a simplestructure, an open interface, and adequate power consumption of aterminal as an upper-level requirement.

SUMMARY

Implementations are disclosed herein that enable triggering atransmission carrier selection in a wireless communication system.

One general aspect includes a method performed by a user equipment (UE)in a wireless communication system, the method including: selecting tocreate a configured sidelink grant corresponding to transmissions of atleast one media access control (MAC) protocol data unit (PDU). Themethod also includes triggering a transmission carrier selectionprocedure based on (i) data being available in a sidelink trafficchannel (STCH) associated with one or more carriers, and (ii) therebeing no configured sidelink grant on any carrier, among the one or morecarriers, that is allowed for the STCH. Other embodiments of this aspectinclude corresponding computer systems, apparatus, and computer programsrecorded on one or more computer storage devices, each configured toperform the actions of the methods.

Implementations may include one or more of the following features. Themethod where the method is performed by a MAC entity of the UE. Themethod where the MAC entity of the UE is configured by an upper layer ofthe UE to transmit using pools of resources in the one or more carriersbased on sensing, or partial sensing, or random selection. The methodwhere the upper layer of the UE is a radio resource control (RRC) layerof the UE. The method where the data being available in the STCHassociated with the one or more carriers and there being no configuredsidelink grant on any carrier allowed for the STCH indicates that thedata available in the STCH is not associated with a selected carrieramong the one or more carriers. The method where an association betweenthe STCH and the one or more carriers is configured by at least one of anetwork or a pre-configuration. The method where the STCH is allowed tobe transmitted in at least one carrier among the one or more carriersbased on at least one of a channel busy ratio (CBR) or a proximity-basedservices (ProSe) per-packet priority (PPPP) of the STCH. The methodfurther including: transmitting the STCH in at least one carrier, amongthe at least one carrier, transmission carrier selection procedure.Implementations of the described techniques may include hardware, amethod or process, or computer software on a computer-accessible medium.

Another general aspect includes a user equipment (UE) configured tooperate in a wireless communication system, the UE including: atransceiver. The user equipment also includes at least one memory; andat least one processor operably connectable to the at least one memoryand storing instructions that, when executed by the at least oneprocessor, perform operations including: selecting to create aconfigured sidelink grant corresponding to transmissions of at least onemedia access control (MAC) protocol data unit (PDU). The user equipmentwhere the operations also include triggering a transmission carrierselection procedure based on (i) data being available in a sidelinktraffic channel (STCH) associated with one or more carriers, and (ii)there being no configured sidelink grant on any carrier, among the oneor more carriers, that is allowed for the STCH. Other embodiments ofthis aspect include corresponding computer systems, apparatus, andcomputer programs recorded on one or more computer storage devices, eachconfigured to perform the actions of the methods.

Implementations may include one or more of the following features. TheUE where the operations are performed by a MAC entity of the UE. The UEwhere the MAC entity of the UE is configured by an upper layer of the UEto transmit using pools of resources in the one or more carriers basedon sensing, or partial sensing, or random selection. The UE where theupper layer of the UE is a radio resource control (RRC) layer of the UE.The UE where the data being available in the STCH associated with theone or more carriers and there being no configured sidelink grant on anycarrier allowed for the STCH indicates that the data available in theSTCH is not associated with a selected carrier among the one or morecarriers. The UE where an association between the STCH and the one ormore carriers is configured by at least one of a network or apre-configuration. The UE where the STCH is allowed to be transmitted inat least one carrier among the one or more carriers based on at leastone of a channel busy ratio (CBR) or a proximity-based services (ProSe)per-packet priority (PPPP) of the STCH. The UE where the operationsfurther include: transmitting, via the at least one transceiver, theSTCH in at least one carrier, among the at least one carrier,transmission carrier selection procedure. Implementations of thedescribed techniques may include hardware, a method or process, orcomputer software on a computer-accessible medium.

Another general aspect includes an apparatus including: at least onememory; and at least one processor operably connectable to the at leastone memory and storing instructions that, when executed by the at leastone processor, perform operations including: selecting to create aconfigured sidelink grant corresponding to transmissions of at least onemedia access control (MAC) protocol data unit (PDU). The apparatus wherethe operations also include triggering a transmission carrier selectionprocedure based on (i) data being available in a sidelink trafficchannel (STCH) associated with one or more carriers, and (ii) therebeing no configured sidelink grant on any carrier, among the one or morecarriers, that is allowed for the STCH.

Other embodiments of this aspect include corresponding computer systems,apparatus, and computer programs recorded on one or more computerstorage devices, each configured to perform the actions of the methods.

All or part of the features described throughout this disclosure may beimplemented as a computer program product including instructions thatare stored on one or more non-transitory machine-readable storage media,and that are executable on one or more processing devices. All or partof the features described throughout this disclosure may be implementedas an apparatus, method, or electronic system that can include one ormore processing devices and memory to store executable instructions toimplement the stated functions.

The details of one or more implementations of the subject matter of thisdisclosure are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages of thesubject matter will become apparent from the description, the drawings,and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a wireless communication system to whichtechnical features of the present disclosure can be applied;

FIG. 2 shows another example of a wireless communication system to whichtechnical features of the present disclosure can be applied;

FIG. 3 shows a block diagram of an example of a user plane protocolstack to which technical features of the present disclosure can beapplied;

FIG. 4 shows a block diagram of an example of a control plane protocolstack to which technical features of the present disclosure can beapplied;

FIG. 5 shows an example of triggering TX carrier (re-)selectionaccording to an implementation of the present disclosure;

FIG. 6 shows an example of a user equipment (UE) accordingimplementations of the present disclosure;

FIG. 7 shows an example of further details of a UE according toimplementations of the present disclosure; and

FIG. 8 shows an example of a network node according to implementationsof the present disclosure.

DETAILED DESCRIPTION

Vehicle-to-everything (V2X) communication is the communication ofinformation from a vehicle to an entity that may affect the vehicle, andvice versa. Examples of V2X include vehicle-to-infrastructure (V2I),vehicle-to-network (V2N), vehicle-to-vehicle (V2V),vehicle-to-pedestrian (V2P), vehicle-to-device (V2D), andvehicle-to-grid (V2G).

V2X systems may be designed to achieve various objectives, such as roadsafety, traffic efficiency, and energy savings. V2X communicationtechnology may be classified into two types, depending on the underlyingtechnology: wireless local area network (WLAN)-based V2X, andcellular-based V2X.

In some V2X systems, V2X sidelink communication may be supported.Furthermore, some V2X sidelink communications may support carrieraggregation (CA). In scenarios where V2X sidelink communicationimplements CA, during actual transmission, a carrier may be initiallyselected or may be re-selected among the aggregated carriers. There maybe various conditions for triggering carrier (re-)selection in such V2Xsidelink CA scenarios. In some scenarios, conditions for triggeringsidelink resource selection may be used as conditions for triggeringtransmission carrier (re-)selection. However, other types of triggeringconditions may be implemented for transmission carrier (re-)selection.

Implementations are disclosed herein that enable new types of triggeringconditions for transmission carrier selection in a wirelesscommunication system. According to some implementation of the presentdisclosure, new triggering conditions for TX carrier (re-)selection areimplemented. For example, a new triggering condition may be implementedsuch that (i) even if an upper layer configures multiple carriers for afirst V2X service and the MAC entity selects a carrier among thosemultiple configured carriers, and (ii) if new data for a second V2Xservice is available in a logical channel which is not associated withthat currently selected carrier, then the TX carrier (re-)selection istriggered and a new carrier for the second V2X service may be selected.

The 3rd generation partnership project (3GPP) long-term evolution (LTE)is a technology designed to enable high-speed packet communications. Inaddition, the international telecommunication union (ITU) and 3GPP havedeveloped technical standards for new radio (NR) systems. In doing so,technology is being identified and developed to successfully standardizethe new radio access technology (RAT), in order to timely satisfy bothurgent market needs, as well as longer-term goals and requirements setforth by the ITU radio communication sector (ITU-R) international mobiletelecommunications (IMT)-2020 process. In some scenarios, NR is beingdesigned to use any spectrum band ranging at least up to 100 GHz, whichmay be made available for wireless communications even in a more distantfuture.

The NR targets a technical framework addressing various usage scenarios,requirements, and deployment scenarios, such as, for example, enhancedmobile broadband (eMBB), massive machine-type-communications (mMTC),ultra-reliable and low latency communications (URLLC), etc.

In some systems, one or more technical features described below may becompatible with one or more technical standards, such as those used by acommunication standard by the 3rd generation partnership project (3GPP)standardization organization, a communication standard by the instituteof electrical and electronics engineers (IEEE), etc. For example, thecommunication standards by the 3GPP standardization organization includelong-term evolution (LTE) and/or evolution of LTE systems. The evolutionof LTE systems includes LTE-advanced (LTE-A), LTE-A Pro, and/or 5G newradio (NR). The communication standard by the IEEE standardizationorganization includes a wireless local area network (WLAN) system suchas IEEE 802.11a/b/g/n/ac/ax. The above system uses various multipleaccess technologies such as orthogonal frequency division multipleaccess (OFDMA) and/or single carrier frequency division multiple access(SC-FDMA) for downlink (DL) and/or uplink (DL). For example, only OFDMAmay be used for DL and only SC-FDMA may be used for UL. Alternatively,OFDMA and SC-FDMA may be used for DL and/or UL.

In this document, the term “/” and “,” should be interpreted to indicate“and/or.” For instance, the expression “A/B” may mean “A and/or B.”Further, “A, B” may mean “A and/or B.” Further, “A/B/C” may mean “atleast one of A, B, and/or C.” Also, “A, B, C” may mean “at least one ofA, B, and/or C.”

FIG. 1 shows an example of a wireless communication system to whichtechnical features of the present disclosure can be applied. In somescenarios, the system of FIG. 1 may be compatible with an evolved-UMTSterrestrial radio access network (E-UTRAN). LTE may be a part of anevolved-UTMS (e-UMTS) using the E-UTRAN.

Referring to FIG. 1, the wireless communication system includes one ormore user equipment (UE; 10), an E-UTRAN and an evolved packet core(EPC). As an example, the UE 10 may be a communication equipment carriedby a user. The UE 10 may be fixed or mobile. The UE 10 may be referredto by various terminologies, such as a mobile station (MS), a userterminal (UT), a subscriber station (SS), a wireless device, etc.

The E-UTRAN consists of one or more base stations (BSs), such as BS 20.The BS 20 provides the E-UTRA user plane and control plane protocolterminations towards the UE 10. In some implementations, the BS 20 maybe a fixed station that communicates with the UE 10. The BS 20 may hostvarious functions, such as, for example, inter-cell radio resourcemanagement (MME), radio bearer (RB) control, connection mobilitycontrol, radio admission control, measurement configuration/provision,dynamic resource allocation (scheduler), etc. The BS may be referred tousing various terminologies, such as an evolved NodeB (eNB), a basetransceiver system (BTS), an access point (AP), etc.

A downlink (DL) denotes communication from the BS 20 to the UE 10. Anuplink (UL) denotes communication from the UE 10 to the BS 20. Asidelink (SL) denotes communication between the UEs 10. In the DL, atransmitter may be a part of the BS 20, and a receiver may be a part ofthe UE 10. In the UL, the transmitter may be a part of the UE 10, andthe receiver may be a part of the BS 20. In the SL, the transmitter andreceiver may be a part of the UE 10.

The EPC includes a mobility management entity (MME), a serving gateway(S-GW) and a packet data network (PDN) gateway (P-GW). The MME hostsvarious functions, such as, for example, non-access stratum (NAS)security, idle state mobility handling, evolved packet system (EPS)bearer control, etc. The S-GW hosts various functions, such as, forexample, mobility anchoring, etc. The S-GW is a gateway having anE-UTRAN as an endpoint. For convenience, MME/S-GW 30 will be referred toherein simply as a “gateway,” but it is understood that this entityincludes both the MME and S-GW. The P-GW hosts various functions, suchas, for example, UE Internet protocol (IP) address allocation, packetfiltering, etc. The P-GW is a gateway having a PDN as an endpoint. TheP-GW is connected to an external network.

The UE 10 is connected to the BS 20 by an interface, such as the Uuinterface. The UEs 10 are interconnected with each other by aninterface, such as the PC5 interface. The BSs 20 are interconnected witheach other by an interface, such as the X2 interface. The BSs 20 arealso connected by the S1 interface to the EPC, more specifically may beconnected to the MME by the S1-MME interface and may be connected to theS-GW by the S1-U interface. In some implementations, the S1 interfacesupports a many-to-many relation between MMEs, S-GWs, and BSs.

FIG. 2 shows another example of a wireless communication system to whichtechnical features of the present disclosure can be applied.Specifically, FIG. 2 shows a system architecture based on a 5G new radioaccess technology (NR) system. The entity used in the 5G NR system(hereinafter, simply referred to as “NR”) may implement some or all ofthe functions of the entities introduced in FIG. 1 (e.g., the eNB, MME,S-GW). The entity used in the NR system may be identified by the name“NG.”

Referring to FIG. 2, the wireless communication system includes one ormore UE 11, a next-generation RAN (NG-RAN) and a 5th generation corenetwork (5GC). The NG-RAN consists of at least one NG-RAN node. TheNG-RAN node may be, for example, an entity corresponding to the BS 20shown in FIG. 1. The NG-RAN node consists of at least one gNB 21 and/orat least one ng-eNB 22. The gNB 21 provides NR user plane and controlplane protocol terminations towards the UE 11. The ng-eNB 22 providesE-UTRA user plane and control plane protocol terminations towards the UE11.

The 5GC includes an access and mobility management function (AMF), auser plane function (UPF) and a session management function (SMF). TheAMF hosts various functions, such as, for example, NAS security, idlestate mobility handling, etc. The AMF hosts various functions, such as,for example, non-access stratum (NAS) security, idle state mobilityhandling, evolved packet system (EPS) bearer control, etc. The UPF hostsvarious functions, such as, for example, mobility anchoring, protocoldata unit (PDU) handling. The UPF hosts various functions, such as, forexample, mobility anchoring, etc. The SMF hosts various functions, suchas, for example, UE IP address allocation, PDU session control, etc.

The gNBs and ng-eNBs are interconnected with each other by an interface,such as the Xn interface. The gNBs and ng-eNBs are also connected by NGinterfaces to the 5GC, for example, to the AMF by the NG-C interface andto the UPF by the NG-U interface.

An example of a protocol structure between network entities describedabove is described. In the examples of FIG. 1 and/or FIG. 2, layers of aradio interface protocol between the UE and the network (e.g. NG-RANand/or E-UTRAN) may be classified into a first layer (L1), a secondlayer (L2), and a third layer (L3), for example based on the lower threelayers of the open system interconnection (OSI) model.

FIG. 3 shows a block diagram of an example of a user plane protocolstack to which technical features of the present disclosure can beapplied. FIG. 4 shows a block diagram of an example of a control planeprotocol stack to which technical features of the present disclosure canbe applied.

Referring to the examples of FIG. 3 and FIG. 4, a physical (PHY) layerbelongs to L1. The PHY layer offers information transfer services to themedia access control (MAC) sublayer and higher layers. For example, thePHY layer offers transport channels to the MAC sublayer, and databetween the MAC sublayer and the PHY layer is transferred via thetransport channels. Between different PHY layers, e.g., between a PHYlayer of a transmission side and a PHY layer of a reception side, datais transferred via physical channels.

The MAC sublayer belongs to L2. The services and functions of the MACsublayer include, for example, mapping between logical channels andtransport channels, multiplexing/de-multiplexing of MAC service dataunits (SDUs) belonging to one or different logical channels into/fromtransport blocks (TB) delivered to/from the physical layer on transportchannels, scheduling information reporting, error correction throughhybrid automatic repeat request (HARM), priority handling between UEs bydynamic scheduling, priority handling between logical channels of one UEby logical channel prioritization (LCP), etc. The MAC sublayer offers tothe radio link control (RLC) sublayer logical channels.

The RLC sublayer belong to L2. In some implementations, the RLC sublayersupports different transmission modes, e.g., transparent mode (TM),unacknowledged mode (UM), and acknowledged mode (AM). The differenttransmission modes may help guarantee various quality of services (QoS)required by radio bearers. The services and functions of the RLCsublayer may depend on the transmission mode. For example, in someimplementations, the RLC sublayer provides transfer of upper layer PDUsfor all three modes, but provides error correction through ARQ for AMonly. In some implementations, such as implementations compatible withLTE/LTE-A, the RLC sublayer provides concatenation, segmentation andreassembly of RLC SDUs (only for UM and AM data transfer) andre-segmentation of RLC data PDUs (only for AM data transfer). In NR, theRLC sublayer provides segmentation (only for AM and UM) andre-segmentation (only for AM) of RLC SDUs and reassembly of SDU (onlyfor AM and UM). In some implementations, the NR does not supportconcatenation of RLC SDUs. The RLC sublayer offers RLC channels to thepacket data convergence protocol (PDCP) sublayer.

The PDCP sublayer belongs to L2. The services and functions of the PDCPsublayer for the user plane include, for example, header compression anddecompression, transfer of user data, duplicate detection, PDCP PDUrouting, retransmission of PDCP SDUs, ciphering and deciphering, etc.The services and functions of the PDCP sublayer for the control planeinclude, for example, ciphering and integrity protection, transfer ofcontrol plane data, etc.

The service data adaptation protocol (SDAP) sublayer belongs to L2. Insome implementations, the SDAP sublayer is only defined in the userplane. The services and functions of SDAP include, for example, mappingbetween a QoS flow and a data radio bearer (DRB), and marking QoS flowID (QFI) in both DL and UL packets. The SDAP sublayer offers QoS flowsto 5GC.

A radio resource control (RRC) layer belongs to L3. In someimplementations, the RRC layer is only defined in the control plane. TheRRC layer controls radio resources between the UE and the network. Forexample, the RRC layer exchanges RRC messages between the UE and the BS.The services and functions of the RRC layer include, for example,broadcast of system information related to access stratum (AS) andnon-access stratum (NAS), paging, establishment, maintenance and releaseof an RRC connection between the UE and the network, security functionsincluding key management, establishment, configuration, maintenance andrelease of radio bearers, mobility functions, QoS management functions,UE measurement reporting and control of the reporting, NAS messagetransfer to/from NAS from/to UE.

As such, in some implementations, the RRC layer controls logicalchannels, transport channels, and physical channels in relation to theconfiguration, reconfiguration, and release of radio bearers. A radiobearer refers to a logical path provided by L1 (PHY layer) and L2(MAC/RLC/PDCP/SDAP sublayer) for data transmission between a UE and anetwork. In some scenarios, setting the radio bearer may includedefining the characteristics of the radio protocol layer and the channelfor providing a specific service, and setting each specific parameterand operation method. Radio bearers may include signaling RB (SRB) anddata RB (DRB). The SRB is used as a path for transmitting RRC messagesin the control plane, and the DRB is used as a path for transmittinguser data in the user plane.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. In some implementations, suchas implementations compatible with LTE/LTE-A, when the RRC connection isestablished between the RRC layer of the UE and the RRC layer of theE-UTRAN, the UE is in the RRC connected state (RRC_CONNECTED); andotherwise, the UE is in the RRC idle state (RRC_IDLE). Inimplementations compatible with NR, the RRC inactive state(RRC_INACTIVE) is additionally introduced. The RRC_INACTIVE state may beused for various purposes. For example, in some scenarios, massivemachine-type communications (MMTC) UEs can be efficiently managed inRRC_INACTIVE. When specific conditions are satisfied, transitions can bemade from one of the above three states to others.

Various operations may be performed according to the RRC state. Forexample, in RRC_IDLE, operations such as public land mobile network(PLMN) selection, broadcast of system information (SI), cellre-selection mobility, core network (CN) paging and discontinuousreception (DRX) configured by NAS may be performed. The UE may beallocated an identifier (ID) which uniquely identifies the UE in atracking area. In some implementations, no RRC context is stored in thebase station.

As another example, in RRC_CONNECTED, the UE has an RRC connection withthe network (i.e. E-UTRAN/NG-RAN). Network-CN connection (bothC/U-planes) is also established for UE. In some implementations, the UEAS context is stored in the network and the UE. The RAN knows the cellwhich the UE belongs to, and the network can transmit and/or receivedata to/from UE. In some implementations, network controlled mobilityincluding measurement is also performed.

One or more operations that are performed in RRC_IDLE may also beperformed in RRC_INACTIVE. However, in some implementations, instead ofperforming CN paging as in RRC_IDLE, RAN paging may be performed inRRC_INACTIVE. For example, in RRC_IDLE, paging for mobile terminated(MT) data is initiated by a core network and paging area is managed bythe core network. In RRC_INACTIVE, paging may be initiated by NG-RAN,and RAN-based notification area (RNA) is managed by NG-RAN. Further, insome implementations, instead of DRX for CN paging configured by NAS inRRC_IDLE, DRX for RAN paging is configured by NG-RAN in RRC_INACTIVE. Insome implementations, in RRC_INACTIVE, 5GC-NG-RAN connection (bothC/U-planes) is established for UE, and the UE AS context is stored inNG-RAN and the UE. The NG-RAN may know the RNA which the UE belongs to.

The NAS layer is implemented above the RRC layer, as shown in theexample of FIG. 4. The NAS control protocol performs various functions,such as, for example, authentication, mobility management, securitycontrol, etc.

Physical channels, for example as utilized by the PHY layer, may bemodulated according to various modulation techniques utilizing time andfrequency as radio resources. For example, the physical channels mayconsist of a plurality of orthogonal frequency division multiplexing(OFDM) symbols in time domain and a plurality of subcarriers infrequency domain. A subframe may be implemented, which consists of aplurality of OFDM symbols in the time domain. A resource block may beimplemented as a resource allocation unit, and each resource block mayconsist of a plurality of OFDM symbols and a plurality of subcarriers.In addition, each subframe may use specific subcarriers of specific OFDMsymbols (e.g., the first OFDM symbol) of the corresponding subframe fora specific purpose, such as for a physical downlink control channel(PDCCH), e.g., an L1/L2 control channel. A transmission time interval(TTI) may be implemented as a basic unit of time, for example as used bya scheduler for resource allocation. The TTI may be defined in units ofone or a plurality of slots, or may be defined in units of mini-slots.

Transport channels may be classified according to how and with whatcharacteristics data are transferred over the radio interface. Forexample, DL transport channels include a broadcast channel (BCH) usedfor transmitting system information, a downlink shared channel (DL-SCH)used for transmitting user traffic or control signals, and a pagingchannel (PCH) used for paging a UE. As another example, UL transportchannels include an uplink shared channel (UL-SCH) for transmitting usertraffic or control signals and a random access channel (RACH) normallyused for initial access to a cell.

Different kinds of data transfer services may be offered by the MACsublayer. Different logical channel types may be defined by what type ofinformation is transferred. In some implementations, logical channelsmay be classified into two groups: control channels and trafficchannels.

Control channels are used for the transfer of control plane informationonly, according to some implementations. The control channels mayinclude, for example, a broadcast control channel (BCCH), a pagingcontrol channel (PCCH), a common control channel (CCCH) and a dedicatedcontrol channel (DCCH). The BCCH is a DL channel for broadcasting systemcontrol information. The PCCH is DL channel that transfers paginginformation, system information change notifications. The CCCH is achannel for transmitting control information between UEs and network. Insome implementations, the CCCH is used for UEs having no RRC connectionwith the network. The DCCH is a point-to-point bi-directional channelthat transmits dedicated control information between a UE and thenetwork. In some implementations, the DCCH is used by UEs having an RRCconnection.

Traffic channels are used for the transfer of user plane informationonly, according to some implementations. The traffic channels include,for example, a dedicated traffic channel (DTCH). The DTCH is apoint-to-point channel, dedicated to one UE, for the transfer of userinformation. In some implementations, the DTCH can exist in both UL andDL.

In some scenarios, mappings may be implemented between the logicalchannels and transport channels. For example, in DL, BCCH can be mappedto BCH, BCCH can be mapped to DL-SCH, PCCH can be mapped to PCH, CCCHcan be mapped to DL-SCH, DCCH can be mapped to DL-SCH, and DTCH can bemapped to DL-SCH. As another example, in UL, CCCH can be mapped toUL-SCH, DCCH can be mapped to UL-SCH, and DTCH can be mapped to UL-SCH.

Examples of sidelink communication are described next. These techniquesmay encompass certain aspects of V2X sidelink communication, but are notlimited thereto. Sidelink communication in the scenario of V2Xcommunications (V2X sidelink communication) will be provided furtherbelow, following the description of more general sidelink communication.

In some implementations, the examples of sidelink communicationdescribed below may be compliant with 3GPP technical standard TS 36.300V15.0.0 (2017 December), Section 23.10. In some scenarios, sidelinkcommunication generally encompasses a UE to UE interface for sidelinkcommunication, vehicle-to-everything (V2X) sidelink communication andsidelink discovery. In some implementations, the sidelink corresponds tothe PC5 interface. Sidelink transmissions may be defined for sidelinkdiscovery, sidelink communication, and V2X sidelink communicationbetween UEs. In some implementations, sidelink transmissions use thesame frame structure as the frame structure that is defined for UL andDL when UEs are in network coverage. However, in some scenarios, thesidelink transmission may be restricted to a sub-set of the UL resourcesin the time and frequency domains. Various physical channels, transportchannels, and logical channels may be implemented and utilized forsidelink transmission.

In some implementations, sidelink communication is a mode ofcommunication whereby UEs can communicate with each other directly overthe PC5 interface. This communication mode is supported when the UE isserved by E-UTRAN and when the UE is outside of E-UTRA coverage. In somescenarios, only those UEs authorized to be used for public safetyoperation can perform sidelink communication. The terminology “sidelinkcommunication” without “V2X” prefix may, in some scenarios, only concernpublic safety unless specifically stated otherwise.

In order to perform synchronization for out of coverage operation, theUE(s) may act as a synchronization source by transmitting a sidelinkbroadcast control channel (SBCCH) and a synchronization signal. In somescenarios, SBCCH carries the most essential system information needed toreceive other sidelink channels and signals. In some implementations,SBCCH along with a synchronization signal is transmitted with a fixedperiodicity of 40 ms. When the UE is in network coverage, the contentsof SBCCH may be derived from the parameters signaled by the BS. When theUE is out of coverage, if the UE selects another UE as a synchronizationreference, then the content of SBCCH may be derived from the receivedSBCCH.

Otherwise, in some implementations, the UE uses pre-configuredparameters. For example, SIB18 provides the resource information for thesynchronization signal and SBCCH transmission. In some scenarios, thereare two pre-configured subframes every 40 ms for out of coverageoperation. The UE may receive the synchronization signal and SBCCH inone subframe and transmit synchronization signal and SBCCH on anothersubframe if the UE becomes a synchronization source based on acriterion.

In some implementations, the UE performs sidelink communication onsubframes defined over the duration of sidelink control (SC) period. TheSC period is the period over which resources allocated in a cell forsidelink control information (SCI) and sidelink data transmissionsoccur. Within the SC period, the UE sends SCI followed by sidelink data.SCI indicates a Layer 1 ID and characteristics of the transmissions(e.g., modulation and coding scheme (MCS), location of the resource(s)over the duration of SC period, timing alignment).

In some implementations, the UE performs transmission and reception overUu and PC5 with the following decreasing priority order in case sidelinkdiscovery gap is not configured:

-   -   Uu transmission/reception (highest priority);    -   PC5 sidelink communication transmission/reception;    -   PC5 sidelink discovery announcement/monitoring (lowest        priority).

In some implementations, the UE performs transmission and reception overUu and PC5 with the following decreasing priority order in case sidelinkdiscovery gap is configured:

-   -   Uu transmission/reception for RACH;    -   PC5 sidelink discovery announcement during a sidelink discovery        gap for transmission;    -   Non-RACH Uu transmission;    -   PC5 sidelink discovery monitoring during a sidelink discovery        gap for reception;    -   Non-RACH Uu reception;    -   PC5 sidelink communication transmission/reception.

A UE supporting sidelink communication may, in some implementations,operate in two modes for resource allocation. The first mode is ascheduled resource allocation mode, which may be referred to as “Mode 1”for resource allocation of sidelink communication. In Mode 1, the UEneeds to be RRC_CONNECTED in order to transmit data. The UE requeststransmission resources from a base station (BS) and the BS schedulestransmission resources for transmission of sidelink control informationand sidelink data. The UE sends a scheduling request (e.g., a dedicatedscheduling request (D-SR) or random access) to the BS followed by asidelink buffer status report (BSR). Based on the sidelink BSR, the BSmay determine that the UE has data for a sidelink communicationtransmission, and may estimate the resources needed for transmission.The BS may then schedule transmission resources for sidelinkcommunication using a configured sidelink radio network temporaryidentity (SL-RNTI). Therefore, in such scenarios, a UE that is in theRRC_CONNECTED state and that is to perform a sidelink communication maysend a sidelink UE information message to a BS. In response, the BS mayconfigure the UE with a SL-RNTI.

The second mode of resource allocation for sidelink communication is aUE autonomous resource selection mode, which may be referred to as “Mode2” for resource allocation of sidelink communication. In Mode 2, a UEselects resources from one or more resource pools and performs selectionof a transport format to transmit sidelink control information and data.In some scenarios, there may be up to 8 transmission resource poolseither pre-configured for out of coverage operation or provided by RRCsignaling for in-coverage operation. Each resource pool may have one ormore priority levels (e.g., one or more ProSe per-packet priority(PPPP)) associated with it. As an example, for transmission of a MACPDU, the UE selects a transmission pool in which one of the associatedPPPP is equal to the PPPP of a logical channel with highest PPPP amongthe logical channel identified in the MAC PDU. In some implementations,it is up to UE implementation how the UE selects amongst multiple poolswith same associated PPPP. There is a one to one association betweensidelink control pool and sidelink data pool. Once the resource pool isselected, in some scenarios, the selection is valid for an entiresidelink control (SC) period. After the SC period is finished, the UEmay perform resource pool selection again. The UE is allowed to performmultiple transmissions to different destinations in a single SC period.

Having provided various examples of general sidelink communicationabove, next, some examples of sidelink communication in the scenario ofV2X communications (V2X sidelink communication) are described.

In some implementations, the techniques of V2X sidelink communicationdescribed below may be compliant with technical standard 3GPP TS 36.300V15.1.0 (2018 March), e.g., Section 23.14. In general, V2X services mayconsist of various types, such as vehicle-to-vehicle (V2V) services,vehicle-to-infrastructure (V2I) services, vehicle-to-nomadic (V2N)services, and vehicle-to-pedestrian (V2P) services.

V2X services may be provided by PC5 interface and/or Uu interface,according to some implementations. Support of V2X services via PC5interface is provided by V2X sidelink communication, which is a mode ofcommunication whereby UEs communicate with each other directly over thePC5 interface. This communication mode is supported when the UE isserved by E-UTRAN and when the UE is outside of E-UTRA coverage. In someimplementations, only UEs that are authorized for V2X services mayperform V2X sidelink communication.

V2X sidelink communication may implement and utilize a user planeprotocol stack and functions for sidelink communication. In addition,according to some implementations of V2X sidelink communication:

-   -   Sidelink traffic channel (STCH) for sidelink communication is        also used for V2X sidelink communication.    -   Non-V2X (e.g., public safety related) data is not multiplexed        with V2X data transmitted in resources configured for V2X        sidelink communication.    -   The access stratum (AS) is provided with the PPPP of a protocol        data unit transmitted over PC5 interface by higher layers. The        packet delay budget (PDB) of the protocol data unit can be        determined from the PPPP. The low PDB is mapped to the high        priority PPPP value.    -   The existing logical channel prioritization based on PPPP is        used for V2X sidelink communication.

Control plane protocol stack for SBCCH for sidelink communication isalso used for V2X sidelink communication.

A UE supporting V2X sidelink communication may, in some implementations,operate in two modes for resource allocation. The first mode is ascheduled resource allocation, which may be referred to as “Mode 3” forresource allocation of V2X sidelink communication. In Mode 3, the UEneeds to be RRC_CONNECTED in order to transmit data. The UE requeststransmission resources from a BS, and the BS schedules transmissionresources for transmission of sidelink control information and data.Sidelink semi-persistent scheduling (SPS) is supported for the Mode 3.

The second mode of resource allocation for V2X sidelink communication isa UE autonomous resource selection, which may be referred to as “Mode 4”for resource allocation of V2X sidelink communication. In Mode 4, the UEselects resources from one or more resource pools and performs selectionof transport format to transmit sidelink control information and data.In scenarios where mapping between the zones and V2X sidelinktransmission resource pools is configured, the UE selects a V2X sidelinkresource pool based on the zone in which the UE is located. The UE mayperform sensing for selection (or re-selection) of sidelink resources.Based on the sensing results, the UE may select (or re-select) specificsidelink resources and may reserve multiple sidelink resources. In somescenarios, up to 2 parallel independent resource reservation processesare allowed to be performed by the UE. The UE is also allowed to performa single resource selection for its V2X sidelink transmission.

An RRC_CONNECTED UE may send a sidelink UE information message to theserving cell if it is interested in V2X sidelink communicationtransmission in order to request sidelink resources.

If the UE is configured by higher layers to receive V2X sidelinkcommunication and V2X sidelink reception resource pools are provided,the UE performs reception on those provided resources.

In some scenarios, reception of sidelink V2X communication in differentcarriers/PLMNs can may supported by having multiple receiver chains inthe UE.

For controlling channel utilization, according to some implementations,the network is able to indicate how the UE adapts its transmissionparameters for each transmission pool depending on a measure ofcongestion on the channel, e.g., a channel busy ratio (CBR). The UE maymeasure all the configured transmission pools including an exceptionalpool. If a pool is (pre)configured such that a UE shall always transmitphysical sidelink control channel (PSCCH) and physical sidelink sharedchannel (PSSCH) in adjacent resource blocks, then the UE measures PSCCHand PSSCH resources together. If a pool is (pre)configured such that aUE may transmit PSCCH and the corresponding PSSCH in non-adjacentresource blocks in a subframe, then PSSCH pool and PSCCH pool aremeasured separately.

A UE in RRC_CONNECTED may be configured to report CBR measurementresults. For CBR reporting, periodic reporting and event triggeredreporting are supported. In some implementations, two types of reportingevents may be utilized for event-triggered CBR reporting. As one type ofreporting event, in scenarios where PSSCH and PSCCH resources are placednon-adjacently, then only PSSCH pool measurement is used forevent-triggered CBR reporting. As another type of reporting event, inscenarios where PSSCH and PSCCH resources are placed adjacently, thenCBR measurement of both the PSSCH and PSCCH resources is used forevent-triggered CBR reporting. In some implementations, CBRevent-triggered reporting is triggered by an overloaded threshold and/ora less-loaded threshold. The network may configure which of thetransmission pools the UE needs to report.

In some implementations, a UE (regardless of its RRC state) performstransmission parameter adaptation based on the measured CBR. Inscenarios where PSSCH and PSCCH resources are placed non-adjacently,only PSSCH pool measurement is used for transmission parameteradaptation. In scenarios where PSSCH and PSCCH resources are placedadjacently, CBR measurement of both the PSSCH and PSCCH resources isused for transmission parameter adaptation. When CBR measurements arenot available, default transmission parameters may be used. Examples ofadapted transmission parameters include maximum transmission power,range of the number of retransmission per TB, range of PSSCH RB number,range of MCS, and maximum limit on channel occupancy ratio. Thetransmission parameter adaption may apply to all transmission poolsincluding an exceptional pool.

Sidelink transmission and/or reception resources including anexceptional pool for different frequencies, for both scheduled resourceallocation and UE autonomous resource selection, may be provided. Thesidelink resources for different frequencies may be provided viadedicated signaling, SIB21 and/or via pre-configuration. The servingcell may indicate to the UE only the frequency on which the UE mayacquire the sidelink resource configuration. If multiple frequencies andassociated resource information are provided, it is up to UEimplementation to select the frequency among the provided frequencies,according to some implementations. In some scenarios, the UE shall notuse preconfigured transmission resource if the UE detects a cellproviding resource configuration or inter-carrier resource configurationfor V2X sidelink communication. Frequencies which may provide V2Xsidelink communication resource configuration or cross-carrierconfiguration may be pre-configured. The RRC_IDLE UE may prioritize thefrequency that provides resource configuration for V2X sidelinkcommunication for other carrier during cell reselection.

If a UE supports multiple transmission chains, then the UE maysimultaneously transmit on multiple carriers via the PC5 interface. Inscenarios where multiple frequencies for V2X are supported, a mappingbetween V2X service types and V2X frequencies is configured by upperlayers. In some implementations, the UE should ensure a V2X service tobe transmitted on the corresponding frequency. For Mode 3, the BS mayschedule a V2X transmission on a frequency based on the sidelink BSR, inwhich the UE includes a destination index that is uniquely associatedwith a frequency reported by the UE to the BS in a sidelink UEinformation message.

In some implementations, V2X communication may also implement featuressuch as transmission (TX) carrier selection, logical channelprioritization, packet duplication, etc. Hereinafter, various aspects ofthe present disclosure are described according to implementations of thepresent disclosure when transmission carrier selection, logical channelprioritization, packet duplication, etc., are considered for V2Xcommunication.

Implementation 1

Conditions for sidelink resource reselection may be used for conditionsfor TX carrier (re-)selection. As examples, TX carrier (re-)selectionmay be autonomously triggered according to conditions such as: (i) ifSL_RESOURCE_RESELECTION_COUNTER=0 and whenSL_RESOURCE_RESELECTION_COUNTER was equal to 1 the MAC entity randomlyselected, with equal probability, a value in the interval [0, 1] whichis above the probability configured by upper layers in probResourceKeep,or (ii) if neither transmission nor retransmission has been performed bythe MAC entity on any resource indicated in the configured sidelinkgrant during the last second, of (iii) if sl-ReselectAfter is configuredand the number of consecutive unused transmission opportunities onresources indicated in the configured sidelink grant is equal tosl-ReselectAfter, or (iv) if there is no configured sidelink grant, or(v) if the configured sidelink grant cannot accommodate a RLC SDU byusing the maximum allowed MCS configured by upper layers in maxMCS-PSSCHand the MAC entity selects not to segment the RLC SDU, or (vi) iftransmission(s) with the configured sidelink grant cannot fulfil thelatency requirement of the data in a sidelink logical channel accordingto the associated PPPP, and the MAC entity selects not to performtransmission(s) corresponding to a single MAC PDU, or (vii) if a pool ofresources is configured or reconfigured by upper layers.

However, in some scenarios, conditions for sidelink resource reselectionmay not sufficiently cover multiple carrier scenarios and multipleservice scenarios. For instance, the MAC entity may be configured byupper layers (e.g., the RRC layer) to transmit using one or multiplepools of resources on multiple carriers, and may perform TX carrierselection among those multiple carriers. In this case, if new data isavailable in a logical channel which is not associated with the selectedcarriers, then there may be a risk that TX carrier selection would notbe triggered.

As a specific example, consider a scenario where an upper layerconfigures multiple carriers for a first V2X service, and the MAC entityselects a particular carrier among those multiple configured carriers.If new data for a second V2X service is available in a logical channelwhich is not associated with the selected particular carrier, then theremay be a risk that the MAC entity cannot trigger TX carrier(re-)selection for the second V2X service, because the multiple carrierswere already configured by the upper layer. To address such problems,according to some implementations of the present disclosure, TX carrierselection should be performed if there is no configured grant on anycarrier allowed for the STCH associated with the sidelink process.

FIG. 5 shows an example of triggering TX carrier (re-)selectionaccording to an implementation of the present disclosure. According tothis example, a new triggering condition may be implemented for TXcarrier (re-)selection.

In step S500, the UE selects to create a configured sidelink grantcorresponding to transmissions of multiple MAC PDUs. In step S510, ifdata is available in a STCH associated with one or multiple carriers andif there is no configured sidelink grant on any carrier, among the oneor multiple carriers, allowed for the STCH, then the UE triggers a TXcarrier (re-) selection procedure.

The above technique may be performed, for example, by a MAC entity of aUE. The MAC entity may be configured by an upper layer to transmit usingpools of resources in the one or multiple carriers based on sensing, orpartial sensing, or random selection. The upper layer may be, forexample, an RRC layer of the UE.

In scenarios where the data available in the STCH is associated with theone or multiple carriers, and where there is no configured sidelinkgrant on any carrier allowed for the STCH, then this may indicate thatthe data available in the STCH is not associated with currently selectedcarrier among the one or multiple carriers. The association between theSTCH and the one or multiple carriers may be configured by a networkand/or may be pre-configured. The STCH may be allowed to be transmittedin at least one carrier among the one or multiple carriers based on CBRand/or PPPP of the STCH.

As such, according to the example in FIG. 5, a new triggering conditionfor TX carrier (re-)selection may be implemented. As a specific example,consider a scenario where an upper layer configures multiple carriersfor a first V2X service, and where the MAC entity selects a particularcarrier among those multiple carriers. If new data for a second V2Xservice is available in a logical channel which is not associated withthe particular carrier that is selected by the MAC entity, then the TXcarrier (re-)selection is triggered, and a new carrier for the secondV2X service can be selected.

As an example of such implementations, TX carrier (re-)selection for V2Xsidelink communication may be performed as follows. In the followingexample, it is assumed that each logical channel may be mapped to eachcarrier or that there may be mapping between carrier(s) and service. Themapping between a logical channel and a carrier may be configured by thenetwork or may be pre-configured. For example, in some implementations,the mapping may be compliant with one or more 3GPP technical standards,e.g., may be configured by the CBR-PPPP table (e.g.,SL-CBR-PPPP-TxConfigList) in Rel-14. With this restriction, in a UE, acertain logical channel may be allowed to be transmitted in restrictedcarriers based on the CBR and the PPPP of the logical channel. Themapping between carriers and services may be configured, for example, bythe core network and the upper layer (e.g., a V2X layer), which mayprovide the mapping information to the AS layer.

In some implementations, the MAC entity may satisfy the following:

1> if the MAC entity is configured by upper layers to transmit using oneor multiple pools of resources on multiple carriers and data isavailable in STCH (e.g., initial TX carrier selection); or

1> if the MAC entity is configured by upper layers to transmit using oneor multiple pools (carriers) of resources on multiple carriers and datais available in STCH not associated with currently selected carriers(e.g., the MAC entity is configured by upper layers to transmit usingone or multiple pools of resources on multiple carriers due to one ormultiple service and data is available in the logical channel which isnot mapped to the currently used carriers); or

1> if the MAC entity is configured by upper layers to transmit using oneor multiple pools of resources on multiple carriers and new pool isconfigured in new carrier (e.g., carrier not configured previously);

2> then for each carrier configured by upper layers and for eachsidelink logical channel where data is available:

3> if the carrier is associated with the sidelink logical channel; andif the CBR of the carrier measured by lower layers, if CBR measurementresults are available, or the corresponding defaultTxConfigIndexconfigured by upper layers for the carrier, if CBR measurement resultsare not available is below threshEnteringCarrier associated with thepriority of the sidelink logical channel;

4> then consider the carrier as a candidate carrier for TX carrier(re-)selection.

1> else if the MAC entity has been configured by upper layers totransmit using one or multiple pools of resources on multiple carriers,and the TX carrier reselection is triggered for a carrier (i.e. TXcarrier reselection):

2> then for each sidelink logical channel mapped to the carrier wheredata is available;

3> if the CBR of the carrier measured by lower layers if CBR measurementresults are available or the corresponding defaultTxConfigIndexconfigured by upper layers for carrier, if CBR measurement results arenot available is above threshLeavingCarrier associated with priority ofsidelink logical channel:

4> then consider the carrier as a candidate carrier for TX carrier(re-)selection; 3> else:

4> for each carrier configured by upper layers, if the CBR of thecarrier measured by lower layers, if CBR measurement results areavailable, or the corresponding defaultTxConfigIndex configured by upperlayers for the carrier, if CBR measurement results are not available isbelow threshEnteringCarrier associated with the priority of the sidelinklogical channel;

5> then consider the carrier as a candidate carrier for TX carrier(re-)selection.

According to some implementations, the MAC entity may also satisfy thefollowing:

1> if more than one carriers are considered as the candidate carriersfor TX carrier (re-) selection, then:

2> select one or more carrier(s) and associated pool(s) of resourcesamong the candidate carriers with increasing order of CBR from thelowest CBR based on the CBR measured by lower layers if CBR measurementresults are available, or the corresponding defaultTxConfigIndexconfigured by upper layers if CBR measurement results are not available;

The UE may, in some implementations, select a limited number of pools ofresources based on UE capability. In some scenarios, it may be up to UEimplementation in terms of how many carriers to select. Continuing withthe above example:

1> else if only one pool of resources is considered as the candidatepool for TX carrier selection or if only one pool of resources isconfigured by upper layers, then:

2> select the carrier and the associated pool of resources.

As another example of implementations of the present disclosure,sidelink grant selection and/or TX carrier (re-)selection for V2Xsidelink communication may be performed as follows.

Sidelink grants may be selected as follows for V2X sidelinkcommunication:

1> if the MAC entity is configured to receive a sidelink grantdynamically on the PDCCH and data is available in STCH, then the MACentity shall:

2> use the received sidelink grant to determine the number of HARQretransmissions and the set of subframes in which transmission of SCIand sidelink shared channel (SL-SCH) occur;

2> consider the received sidelink grant to be a configured sidelinkgrant;

1> if the MAC entity is configured by upper layers to receive a sidelinkgrant on the PDCCH addressed to SL Semi-Persistent Scheduling V2X RNTI(V-RNTI), then the MAC entity shall for each SL SPS configuration:

2> if PDCCH contents indicate SPS activation, then:

3> use the received sidelink grant to determine the number of HARQretransmissions and the set of subframes in which transmission of SCIand SL-SCH occur;

3> consider the received sidelink grant to be a configured sidelinkgrant;

2> if PDCCH contents indicate SPS release, then:

3> clear the corresponding configured sidelink grant;

1> if the MAC entity is configured by upper layers to transmit usingpool(s) of resources in one or multiple carriers based on sensing, orpartial sensing, or random selection only if upper layers indicates thattransmissions of multiple MAC PDUs are allowed, and the MAC entityselects to create a configured sidelink grant corresponding totransmissions of multiple MAC PDUs, and data is available in STCHassociated with one or multiple carriers, then the MAC entity shall foreach Sidelink process configured for multiple transmissions:

2> if there is no configured sidelink grant on any carrier allowed forthe STCH associated with the Sidelink process, then:

3> trigger the TX carrier (re-)selection procedure as specified below;

2> else if there is a configured sidelink grant associated with theSidelink process, then:

3> if SL_RESOURCE_RESELECTION_COUNTER=0 and whenSL_RESOURCE_RESELECTION_COUNTER was equal to 1 the MAC entity randomlyselected, with equal probability, a value in the interval [0, 1] whichis above the probability configured by upper layers in probResourceKeep;or

3> if neither transmission nor retransmission has been performed by theMAC entity on any resource indicated in the configured sidelink grantduring the last second; or

3> if sl-ReselectAfter is configured and the number of consecutiveunused transmission opportunities on resources indicated in theconfigured sidelink grant is equal to sl-ReselectAfter; or

3> if none of the configured sidelink grant(s) on the carrier(s) allowedfor the STCH have radio resources available in this TTI to accommodate aRLC SDU by using the maximum allowed MCS configured by upper layers inmaxMCS-PSSCH and the MAC entity selects not to segment the RLC SDU; or

3> if none of the configured sidelink grant(s) on the carrier(s) allowedfor the STCH have radio resources available in this TTI, to fulfil thelatency requirement of the data in a sidelink logical channel accordingto the associated PPPP, and the MAC entity selects not to performtransmission(s) corresponding to a single MAC PDU; or

3> if the pool of resources where the sidelink grant is configured forthe Sidelink process, is reconfigured by upper layers, then:

4> clear the configured sidelink grant;

4> trigger the TX carrier (re-)selection procedure as specified below;

2> if the TX carrier (re-)selection procedure is triggered in above andthe carrier is (re-) selected in the TX carrier (re-)selection, then thefollowing is performed on the selected carrier:

3> select one of the allowed values configured by upper layers inrestrictResourceReservationPeriod and set the resource reservationinterval by multiplying 100 with the selected value;

3> randomly select, with equal probability, an integer value in theinterval [5, 15] for the resource reservation interval higher than orequal to 100 ms, in the interval [10, 30] for the resource reservationinterval equal to 50 ms or in the interval [25, 75] for the resourcereservation interval equal to 20 ms, and setSL_RESOURCE_RESELECTION_COUNTER to the selected value;

3> select the number of HARQ retransmissions from the allowed numbersthat are configured by upper layers in allowedRetxNumberPSSCH includedin pssch-TxConfigList and, if configured by upper layers, overlapped inallowedRetxNumberPSSCH indicated in cbr-pssch-TxConfigList for thehighest priority of the sidelink logical channel(s) allowed on theselected carrier and the CBR measured by lower layers if CBR measurementresults are available or the corresponding defaultTxConfigIndexconfigured by upper layers if CBR measurement results are not available;

3> select an amount of frequency resources within the range that isconfigured by upper layers between minSubchannel-NumberPSSCH andmaxSubchannel-NumberPSSCH included in pssch-TxConfigList and, ifconfigured by upper layers, overlapped between minSubchannel-NumberPSSCHand maxSubchannel-NumberPSSCH indicated in cbr-pssch-TxConfigList forthe highest priority of the sidelink logical channel(s) allowed on theselected carrier and the CBR measured by lower layers if CBR measurementresults are available or the corresponding defaultTxConfigIndexconfigured by upper layers if CBR measurement results are not available;

3> if transmission based on random selection is configured by upperlayers, then:

4> randomly select the time and frequency resources for one transmissionopportunity from the resource pool, according to the amount of selectedfrequency resources. The random function shall be such that each of theallowed selections can be chosen with equal probability;

3> else:

4> randomly select the time and frequency resources for one transmissionopportunity from the resources indicated by the physical layer,according to the amount of selected frequency resources. The randomfunction shall be such that each of the allowed selections can be chosenwith equal probability;

3> use the randomly selected resource to select a set of periodicresources spaced by the resource reservation interval for transmissionopportunities of SCI and SL-SCH corresponding to the number oftransmission opportunities of MAC PDUs;

3> if the number of HARQ retransmissions is equal to 1 and there areavailable resources left in the resources indicated by the physicallayer that meet the conditions for more transmission opportunities,then:

4> randomly select the time and frequency resources for one transmissionopportunity from the available resources, according to the amount ofselected frequency resources. The random function shall be such thateach of the allowed selections can be chosen with equal probability;

4> use the randomly selected resource to select a set of periodicresources spaced by the resource reservation interval for the othertransmission opportunities of SCI and SL-SCH corresponding to the numberof retransmission opportunities of the MAC PDUs;

4> consider the first set of transmission opportunities as the newtransmission opportunities and the other set of transmissionopportunities as the retransmission opportunities;

4> consider the set of new transmission opportunities and retransmissionopportunities as the selected sidelink grant.

3> else:

4> consider the set as the selected sidelink grant;

3> use the selected sidelink grant to determine the set of subframes inwhich transmissions of SCI and SL-SCH occur;

3> consider the selected sidelink grant to be a configured sidelinkgrant;

2> else if SL_RESOURCE_RESELECTION_COUNTER=0 and whenSL_RESOURCE_RESELECTION_COUNTER was equal to 1 the MAC entity randomlyselected, with equal probability, a value in the interval [0, 1] whichis less than or equal to the probability configured by upper layers inprobResourceKeep, then:

3> clear the configured sidelink grant, if available;

3> randomly select, with equal probability, an integer value in theinterval [5, 15] for the resource reservation interval higher than orequal to 100 ms, in the interval [10, 30] for the resource reservationinterval equal to 50 ms or in the interval [25, 75] for the resourcereservation interval equal to 20 ms, and setSL_RESOURCE_RESELECTION_COUNTER to the selected value;

3> use the previously selected sidelink grant for the number oftransmissions of the MAC PDUs with the resource reservation interval todetermine the set of subframes in which transmissions of SCI and SL-SCHoccur;

3> consider the selected sidelink grant to be a configured sidelinkgrant;

1> else, if the MAC entity is configured by upper layers to transmitusing pool(s) of resources in one or multiple carriers, the MAC entityselects to create a configured sidelink grant corresponding totransmission(s) of a single MAC PDU, and data is available in STCHassociated with one or multiple carriers, then the MAC entity shall fora Sidelink process:

2> trigger the TX carrier (re-)selection procedure as specified below;

2> if the carrier is (re-)selected in the TX carrier (re-)selection,then the following is performed on the selected carrier:

3> select the number of HARQ retransmissions from the allowed numbersthat are configured by upper layers in allowedRetxNumberPSSCH includedin pssch-TxConfigList and, if configured by upper layers, overlapped inallowedRetxNumberPSSCH indicated in cbr-pssch-TxConfigList for thehighest priority of the sidelink logical channel(s) allowed on theselected carrier and the CBR measured by lower layers if CBR measurementresults are available or the corresponding defaultTxConfigIndexconfigured by upper layers if CBR measurement results are not available;

3> select an amount of frequency resources within the range that isconfigured by upper layers between minSubchannel-NumberPSSCH andmaxSubchannel-NumberPSSCH included in pssch-TxConfigList and, ifconfigured by upper layers, overlapped between minSubchannel-NumberPSSCHand maxSubchannel-NumberPSSCH indicated in cbr-pssch-TxConfigList forthe highest priority of the sidelink logical channel(s) allowed on theselected carrier and the CBR measured by lower layers if CBR measurementresults are available or the corresponding defaultTxConfigIndexconfigured by upper layers if CBR measurement results are not available;

3> if transmission based on random selection is configured by upperlayers, then:

4> randomly select the time and frequency resources for one transmissionopportunity of SCI and SL-SCH from the resource pool, according to theamount of selected frequency resources. The random function shall besuch that each of the allowed selections can be chosen with equalprobability;

3> else:

4> randomly select the time and frequency resources for one transmissionopportunity of SCI and SL-SCH from the resources indicated by thephysical layer, according to the amount of selected frequency resources.The random function shall be such that each of the allowed selectionscan be chosen with equal probability;

3> if the number of HARQ retransmissions is equal to 1, then:

4> if transmission based on random selection is configured by upperlayers and there are available resources that meet the conditions forone more transmission opportunity, then:

5> randomly select the time and frequency resources for the othertransmission opportunity of SCI and SL-SCH corresponding to additionaltransmission of the MAC PDU from the available resources, according tothe amount of selected frequency resources. The random function shall besuch that each of the allowed selections can be chosen with equalprobability;

4> else, if transmission based on sensing or partial sensing isconfigured by upper layers and there are available resources left in theresources indicated by the physical layer that meet the conditions forone more transmission opportunity, then:

5> randomly select the time and frequency resources for the othertransmission opportunity of SCI and SL-SCH corresponding to additionaltransmission of the MAC PDU from the available resources, according tothe amount of selected frequency resources. The random function shall besuch that each of the allowed selections can be chosen with equalprobability;

4> consider a transmission opportunity which comes first in time as thenew transmission opportunity and a transmission opportunity which comeslater in time as the retransmission opportunity;

4> consider both of the transmission opportunities as the selectedsidelink grant;

3> else:

4> consider the transmission opportunity as the selected sidelink grant;

3> use the selected sidelink grant to determine the subframes in whichtransmission(s) of SCI and SL-SCH occur;

3> consider the selected sidelink grant to be a configured sidelinkgrant.

For V2X sidelink communication, according to some implementations, theUE may ensure that the randomly selected time and frequency resourcesfulfil a latency requirement.

For example, in some implementations, the MAC entity shall, for eachsubframe:

1> for each configured sidelink grant occurring in this subframe:

2> if SL_RESOURCE_RESELECTION_COUNTER=1 for the Sidelink processassociated with the configured sidelink grant and the MAC entityrandomly selected, with equal probability, a value in the interval [0,1] which is above the probability configured by upper layers inprobResourceKeep, then:

3> set the resource reservation interval for the configured sidelinkgrant equal to 0;

2> if the configured sidelink grant corresponds to transmission of SCI,then:

3> for V2X sidelink communication in UE autonomous resource selection:

4> select a MCS which is, if configured, within the range that isconfigured by upper layers between minMCS-PSSCH and maxMCS-PSSCHincluded in pssch-TxConfigList and, if configured by upper layers,overlapped between minMCS-PSSCH and maxMCS-PSSCH indicated incbr-pssch-TxConfigList for the highest priority of the sidelink logicalchannel(s) in the MAC PDU and the CBR measured by lower layers if CBRmeasurement results are available or the correspondingdefaultTxConfigIndex configured by upper layers if CBR measurementresults are not available;

3> for V2X sidelink communication in scheduled resource allocation:

4> select a MCS unless it is configured by upper layer;

3> instruct the physical layer to transmit SCI corresponding to theconfigured sidelink grant;

3> for V2X sidelink communication, deliver the configured sidelinkgrant, the associated HARQ information and the value of the highestpriority of the sidelink logical channel(s) in the MAC PDU to theSidelink HARQ Entity for this subframe;

2> else if the configured sidelink grant corresponds to transmission offirst transport block for sidelink communication, then:

3> deliver the configured sidelink grant and the associated HARQinformation to the Sidelink HARQ Entity for this subframe.

TX carrier (re-)selection for V2X sidelink communication, according tosome implementations, is performed as follows. The MAC entity shallconsider a CBR of a carrier to be one measured by lower layers if CBRmeasurement results are available, or the correspondingdefaultTxConfigIndex configured by upper layers for the carrier if CBRmeasurement results are not available.

If the TX carrier (re-)selection is triggered for a Sidelink process,then the MAC entity shall:

1> if there is no configured sidelink grant on any carrier allowed forthe sidelink logical channel where data is available, then:

2> for each carrier configured by upper layers associated with theconcerned sidelink logical channel:

3> if the CBR of the carrier is below threshCBR-FreqReselectionassociated with the priority of the sidelink logical channel, then:

4> consider the carrier as a candidate carrier for TX carrier(re-)selection for the concerned sidelink logical channel.

1> else:

2> for each sidelink logical channel allowed on the carrier where datais available and TX carrier (re-)selection is triggered:

3> if the CBR of the carrier is below threshCBR-FreqKeeping associatedwith priority of sidelink logical channel, then:

4> select the carrier and the associated pool of resources.

3> else:

4> for each carrier configured by upper layers, if the CBR of thecarrier is below threshCBR-FreqReselection associated with the priorityof the sidelink logical channel;

5> consider the carrier as a candidate carrier for TX carrier(re-)selection.

The MAC entity, according to some implementations, shall satisfy thefollowing:

1> if one or more carriers are considered as the candidate carriers forTX carrier (re-) selection, then:

2> for each sidelink logical channel allowed on the carrier where datais available and TX carrier (re-)selection is triggered, select one ormore carrier(s) and associated pool(s) of resources among the candidatecarriers with increasing order of CBR from the lowest CBR.

Implementation 2

In some communication systems, the selection of a modulation and codingscheme (MCS) is irrelevant for service. However, in some scenarios, 64quadrature amplitude modulation (64-QAM) may be applicable for certainservices. Accordingly, in some implementations of the presentdisclosure, the criteria for resource reselection triggering may bemodified.

For example, according to an implementation, if the configured sidelinkgrant cannot accommodate a RLC SDU by using a lower MCS between themaximum allowed MCS configured by upper layers in maxMCS-PSSCH and themaximum allowed MCS of the STCH corresponding to the RLC SDU, and if theMAC entity selects not to segment the RLC SDU, then resource reselectionand/or TX carrier (re-)selection may be triggered. If an upper layerdoes not provide the maximum allowed MCS of the STCH corresponding tothe RLC SDU, then the maximum allowed MCS of the STCH corresponding tothe RLC SDU may be set to 16QAM. If the configured sidelink grant cannotaccommodate the RLC SDU, then according to some implementations, it maybe left for UE implementation whether to perform segmentation orsidelink resource reselection.

Alternatively, in some implementations, if 64-QAM is allowed by upperlayer configuration for the STCH corresponding to the RLC SDU, and ifthe configured sidelink grant cannot accommodate a RLC SDU by using64QAM and the MAC entity selects not to segment the RLC SDU, then thesidelink process configured for multiple transmissions may triggerresource reselection and/or TX carrier (re-)selection. Otherwise, if theconfigured sidelink grant cannot accommodate a RLC SDU by using themaximum allowed MCS configured by upper layers in maxMCS-PSSCH and ifthe MAC entity selects not to segment the RLC SDU, then the sidelinkprocess configured for multiple transmissions may trigger resourcereselection and/or TX carrier (re-)selection.

As an example implementations of the present disclosure, the MAC entitymay operate as follows.

Sidelink grants may be selected on carrier(s) selected as follows forV2X sidelink communication:

1> if the MAC entity is configured to receive a sidelink grantdynamically on the PDCCH and data is available in STCH, then the MACentity shall:

2> use the received sidelink grant to determine the number of HARQretransmissions and the set of subframes in which transmission of SCIand SL-SCH occur;

2> consider the received sidelink grant to be a configured sidelinkgrant;

1> if the MAC entity is configured by upper layers to receive a sidelinkgrant on the PDCCH addressed to SL Semi-Persistent Scheduling V-RNTI,then the MAC entity shall for each SL SPS configuration:

2> if PDCCH contents indicate SPS activation, then:

3> use the received sidelink grant to determine the number of HARQretransmissions and the set of subframes in which transmission of SCIand SL-SCH occur;

3> consider the received sidelink grant to be a configured sidelinkgrant;

2> if PDCCH contents indicate SPS release, then:

3> clear the corresponding configured sidelink grant;

1> if the MAC entity is configured by upper layers to transmit using oneor multiple pools of resources based on sensing, or partial sensing, orrandom selection only if upper layers indicates that transmissions ofmultiple MAC PDUs are allowed, and the MAC entity selects to create aconfigured sidelink grant corresponding to transmissions of multiple MACPDUs, and data is available in STCH associated with one or multiplecarriers, then the MAC entity shall for each Sidelink process configuredfor multiple transmissions on one of the carriers:

2> if SL_RESOURCE_RESELECTION_COUNTER=0 and whenSL_RESOURCE_RESELECTION_COUNTER was equal to 1 the MAC entity randomlyselected, with equal probability, a value in the interval [0, 1] whichis above the probability configured by upper layers in probResourceKeep;or

2> if neither transmission nor retransmission has been performed by theMAC entity on any resource indicated in the configured sidelink grantduring the last second; or

2> if sl-ReselectAfter is configured and the number of consecutiveunused transmission opportunities on resources indicated in theconfigured sidelink grant is equal to sl-ReselectAfter; or

2> if there is no configured sidelink grant; or

2> if the configured sidelink grant cannot accommodate a RLC SDU byusing a lower MCS between the maximum allowed MCS configured by upperlayers in maxMCS-PSSCH and the maximum allowed MCS of the STCHcorresponding to the RLC SDU and the MAC entity selects not to segmentthe RLC SDU; or

If the upper layer does not provide the maximum allowed MCS of the STCHcorresponding to the RLC SDU, then the maximum allowed MCS of the STCHcorresponding to the RLC SDU is set to 16-QAM, according to someimplementations. If the configured sidelink grant cannot accommodate theRLC SDU, then according to some implementations, then it is left for UEimplementation whether to perform segmentation or sidelink resourcereselection.

2> if transmission(s) with the configured sidelink grant cannot fulfilthe latency requirement of the data in a sidelink logical channelaccording to the associated PPPP, and if the MAC entity selects not toperform transmission(s) corresponding to a single MAC PDU; or

2> if a pool of resources is configured or reconfigured by upper layersand a carrier is reselected, then:

3> trigger the TX carrier (re-)selection procedure;

3> clear the configured sidelink grant, if available;

3> select one of the allowed values configured by upper layers inrestrictResourceReservationPeriod and set the resource reservationinterval by multiplying 100 with the selected value;

3> randomly select, with equal probability, an integer value in theinterval [5, 15] for the resource reservation interval higher than orequal to 100 ms, in the interval [10, 30] for the resource reservationinterval equal to 50 ms or in the interval [25, 75] for the resourcereservation interval equal to 20 ms, and setSL_RESOURCE_RESELECTION_COUNTER to the selected value;

3> select the number of HARQ retransmissions from the allowed numbersthat are configured by upper layers in allowedRetxNumberPSSCH includedin pssch-TxConfigList and, if configured by upper layers, overlapped inallowedRetxNumberPSSCH indicated in cbr-pssch-TxConfigList for thehighest priority of the sidelink logical channel(s) mapped to thecarrier and the CBR measured by lower layers if CBR measurement resultsare available or the corresponding defaultTxConfigIndex configured byupper layers if CBR measurement results are not available;

3> select an amount of frequency resources within the range that isconfigured by upper layers between minSubchannel-NumberPSSCH andmaxSubchannel-NumberPSSCH included in pssch-TxConfigList and, ifconfigured by upper layers, overlapped between minSubchannel-NumberPSSCHand maxSubchannel-NumberPSSCH indicated in cbr-pssch-TxConfigList forthe highest priority of the sidelink logical channel(s) mapped to thecarrier and the CBR measured by lower layers if CBR measurement resultsare available or the corresponding defaultTxConfigIndex configured byupper layers if CBR measurement results are not available;

3> if transmission based on random selection is configured by upperlayers, then:

4> randomly select the time and frequency resources for one transmissionopportunity from the resource pool, according to the amount of selectedfrequency resources. The random function shall be such that each of theallowed selections can be chosen with equal probability;

3> else:

4> randomly select the time and frequency resources for one transmissionopportunity from the resources indicated by the physical layer,according to the amount of selected frequency resources. The randomfunction shall be such that each of the allowed selections can be chosenwith equal probability;

3> use the randomly selected resource to select a set of periodicresources spaced by the resource reservation interval for transmissionopportunities of SCI and SL-SCH corresponding to the number oftransmission opportunities of MAC PDUs;

3> if the number of HARQ retransmissions is equal to 1 and there areavailable resources left in the resources indicated by the physicallayer that meet the conditions for more transmission opportunities,then:

4> randomly select the time and frequency resources for one transmissionopportunity from the available resources, according to the amount ofselected frequency resources. The random function shall be such thateach of the allowed selections can be chosen with equal probability;

4> use the randomly selected resource to select a set of periodicresources spaced by the resource reservation interval for the othertransmission opportunities of SCI and SL-SCH corresponding to the numberof retransmission opportunities of the MAC PDUs;

4> consider the first set of transmission opportunities as the newtransmission opportunities and the other set of transmissionopportunities as the retransmission opportunities;

4> consider the set of new transmission opportunities and retransmissionopportunities as the selected sidelink grant.

3> else:

4> consider the set as the selected sidelink grant;

3> use the selected sidelink grant to determine the set of subframes inwhich transmissions of SCI and SL-SCH occur;

3> consider the selected sidelink grant to be a configured sidelinkgrant;

2> else if SL_RESOURCE_RESELECTION_COUNTER=0 and whenSL_RESOURCE_RESELECTION_COUNTER was equal to 1 the MAC entity randomlyselected, with equal probability, a value in the interval [0, 1] whichis less than or equal to the probability configured by upper layers inprobResourceKeep, then:

3> clear the configured sidelink grant, if available;

3> randomly select, with equal probability, an integer value in theinterval [5, 15] for the resource reservation interval higher than orequal to 100 ms, in the interval [10, 30] for the resource reservationinterval equal to 50 ms or in the interval [25, 75] for the resourcereservation interval equal to 20 ms, and setSL_RESOURCE_RESELECTION_COUNTER to the selected value;

3> use the previously selected sidelink grant for the number oftransmissions of the MAC PDUs with the resource reservation interval todetermine the set of subframes in which transmissions of SCI and SL-SCHoccur;

3> consider the selected sidelink grant to be a configured sidelinkgrant;

1> else, if the MAC entity is configured by upper layers to transmitusing one or multiple pools of resources, the MAC entity selects tocreate a configured sidelink grant corresponding to transmission(s) of asingle MAC PDU, and data is available in STCH associated with one ormultiple carriers, then the MAC entity shall for a Sidelink process onthe carrier:

2> trigger the TX carrier (re-)selection procedure;

2> select the number of HARQ retransmissions from the allowed numbersthat are configured by upper layers in allowedRetxNumberPSSCH includedin pssch-TxConfigList and, if configured by upper layers, overlapped inallowedRetxNumberPSSCH indicated in cbr-pssch-TxConfigList for thehighest priority of the sidelink logical channel(s) mapped to thecarrier and the CBR measured by lower layers if CBR measurement resultsare available or the corresponding defaultTxConfigIndex configured byupper layers if CBR measurement results are not available;

2> select an amount of frequency resources within the range that isconfigured by upper layers between minSubchannel-NumberPSSCH andmaxSubchannel-NumberPSSCH included in pssch-TxConfigList and, ifconfigured by upper layers, overlapped between minSubchannel-NumberPSSCHand maxSubchannel-NumberPSSCH indicated in cbr-pssch-TxConfigList forthe highest priority of the sidelink logical channel(s) mapped to thecarrier and the CBR measured by lower layers if CBR measurement resultsare available or the corresponding defaultTxConfigIndex configured byupper layers if CBR measurement results are not available;

2> if transmission based on random selection is configured by upperlayers, then:

3> randomly select the time and frequency resources for one transmissionopportunity of SCI and SL-SCH from the resource pool, according to theamount of selected frequency resources. The random function shall besuch that each of the allowed selections can be chosen with equalprobability;

2> else:

3> randomly select the time and frequency resources for one transmissionopportunity of SCI and SL-SCH from the resource pool indicated by thephysical layer, according to the amount of selected frequency resources.The random function shall be such that each of the allowed selectionscan be chosen with equal probability;

2> if the number of HARQ retransmissions is equal to 1, then:

3> if transmission based on random selection is configured by upperlayers and there are available resources that meet the conditions forone more transmission opportunity, then:

4> randomly select the time and frequency resources for the othertransmission opportunity of SCI and SL-SCH corresponding to additionaltransmission of the MAC PDU from the available resources, according tothe amount of selected frequency resources. The random function shall besuch that each of the allowed selections can be chosen with equalprobability;

3> else, if transmission based on sensing or partial sensing isconfigured by upper layers and there are available resources left in theresources indicated by the physical layer that meet the conditions forone more transmission opportunity, then:

4> randomly select the time and frequency resources for the othertransmission opportunity of SCI and SL-SCH corresponding to additionaltransmission of the MAC PDU from the available resources, according tothe amount of selected frequency resources. The random function shall besuch that each of the allowed selections can be chosen with equalprobability;

3> consider a transmission opportunity which comes first in time as thenew transmission opportunity and a transmission opportunity which comeslater in time as the retransmission opportunity;

3> consider both of the transmission opportunities as the selectedsidelink grant;

2> else:

3> consider the transmission opportunity as the selected sidelink grant;

2> use the selected sidelink grant to determine the subframes in whichtransmission(s) of SCI and SL-SCH occur;

2> consider the selected sidelink grant to be a configured sidelinkgrant;

For V2X sidelink communication, in some implementations the UE mayensure that the randomly selected time resources and frequency resourcesfulfill a latency requirement.

For example, for V2X sidelink communication, when a UE randomly selectsthe time resources and frequency resources or when the UE uses therandomly selected resource to select a set of periodic resources spacedby the resource reservation interval, then the UE should fulfil thefollowing requirement.

According to some implementations, the MAC entity shall satisfy thefollowing, for each subframe:

1> if the MAC entity has a configured sidelink grant occurring in thissubframe, then:

2> if SL_RESOURCE_RESELECTION_COUNTER=1 and the MAC entity randomlyselected, with equal probability, a value in the interval [0, 1] whichis above the probability configured by upper layers in probResourceKeep,then:

3> set the resource reservation interval equal to 0;

2> if the configured sidelink grant corresponds to transmission of SCI,then:

3> instruct the physical layer to transmit SCI corresponding to theconfigured sidelink grant;

3> for V2X sidelink communication, deliver the configured sidelinkgrant, the associated HARQ information and the value of the highestpriority of the sidelink logical channel(s) in the MAC PDU to theSidelink HARQ Entity for this subframe;

2> else if the configured sidelink grant corresponds to transmission offirst transport block for sidelink communication, then:

3> deliver the configured sidelink grant and the associated HARQinformation to the Sidelink HARQ Entity for this subframe.

In some implementations, hybrid automatic repeat request (HARQ)operations for sidelink communications may be performed as follows. TheMAC entity is configured by upper layers to transmit using pool(s) ofresources on one or multiple carriers, and there is one sidelink HARQentity at the MAC entity for each carrier for transmission on SL-SCH,which maintains a number of parallel sidelink processes.

For V2X sidelink communication, in some implementations, the maximumnumber of transmitting sidelink processes associated with each sidelinkHARQ entity is 8. A sidelink process may be configured for transmissionsof multiple MAC PDUs. For transmissions of multiple MAC PDUs, themaximum number of transmitting sidelink processes with each sidelinkHARQ entity is 2.

In some implementations, a delivered and configured sidelink grant andits associated HARQ information are associated with a sidelink process.

For each subframe of the SL-SCH and each sidelink process, the SidelinkHARQ Entity shall satisfy the following, in some implementations:

1> if a sidelink grant corresponding to a new transmission opportunityhas been indicated for this Sidelink process and there is SL data, forsidelink logical channels of ProSe destination associated with thissidelink grant, available for transmission, then:

2> obtain the MAC PDU from the “Multiplexing and assembly” entity;

2> deliver the MAC PDU and the sidelink grant and the HARQ informationto this Sidelink process;

2> instruct this Sidelink process to trigger a new transmission.

1> else, if this subframe corresponds to retransmission opportunity forthis Sidelink process, then:

2> instruct this Sidelink process to trigger a retransmission.

In some implementations, logical channel prioritization for sidelink maybe performed as follows. The logical channel prioritization procedure isapplied when a new transmission is performed. Each sidelink logicalchannel has an associated priority which is the PPPP and also has anassociated ProSe per-packet reliability (PPPR). Multiple sidelinklogical channels may have the same associated priority. The mappingbetween priority and LCID may be left for UE implementation. Ifduplication is activated, then the MAC entity shall map differentsidelink logical channels in duplication onto different carriers.

The MAC entity shall, in some implementations, perform the followinglogical channel prioritization procedure either for each SCI transmittedin an SC period in sidelink communication, or for each SCI correspondingto a new transmission in V2X sidelink communication:

1> The MAC entity shall allocate resources to the sidelink logicalchannels in the following steps:

2> Only consider sidelink logical channels not previously selected forthis SC period and the SC periods (if any) which are overlapping withthis SC period, to have data available for transmission in sidelinkcommunication.

2> Only consider sidelink logical channels which are allowed on thecarrier where the SCI is transmitted for V2X sidelink communication, ifconfigured by upper layer

2> Exclude sidelink logical channel(s) not mapped to the carrier wherethe SCI is transmitted, if duplication is activated.

2> Step 0: Select a ProSe Destination, having the sidelink logicalchannel with the highest priority, among the sidelink logical channelshaving data available for transmission;

1> For each MAC PDU associated to the SCI:

2> Step 1: Among the sidelink logical channels belonging to the selectedProSe Destination and having data available for transmission, allocateresources to the sidelink logical channel with the highest priority;

2> Step 2: if any resources remain, then sidelink logical channelsbelonging to the selected ProSe Destination are served in decreasingorder of priority until either the data for the sidelink logicalchannel(s) or the SL grant is exhausted, whichever comes first. Sidelinklogical channels configured with equal priority should be servedequally.

1> the UE shall also follow the rules below during the schedulingprocedures above:

2> the UE should not segment an RLC SDU (or partially transmitted SDU)if the whole SDU (or partially transmitted SDU) fits into the remainingresources;

2> if the UE segments an RLC SDU from the sidelink logical channel, thenit shall maximize the size of the segment to fill the grant as much aspossible;

2> the UE should maximize the transmission of data;

2> if the MAC entity is given a sidelink grant size that is equal to orlarger than 10 bytes (for sidelink communication) or 11 bytes (for V2Xsidelink communication) while having data available for transmission,the MAC entity shall not transmit only padding.

Implementation 3

In some communication systems, a reliability level (e.g., PPPR) is notconsidered for buffer status reporting. In such scenarios, an amount ofdata requiring higher reliability (e.g., data having lower PPPR) andlower priority (e.g., data having higher PPPP) data cannot be reported.Such scenarios may result in problems in which data having higherreliability with lower priority would have a lower chance of beingtransmitted.

According to an implementation of the present disclosure, data which hasa reliability level (e.g., PPPR) that is below (and/or equal to) athreshold reliability level may trigger BSR reporting if SL data, for asidelink logical channel of a ProSe Destination, becomes available fortransmission in the RLC entity or in the PDCP entity, and if either thedata belongs to a sidelink logical channel with lower PPPR than thePPPRs of the sidelink logical channels which belong to any LCG belongingto the same ProSe Destination and for which data is already availablefor transmission, or if there is currently no data available fortransmission for any of the sidelink logical channels belonging to thesame ProSe Destination.

Alternatively, the data which has a priority level (e.g., PPPP) that isbelow (and/or equal to) a threshold priority level may trigger BSRreporting if SL data, for a sidelink logical channel of a ProSeDestination, becomes available for transmission in the RLC entity or inthe PDCP entity and if the data belongs to a sidelink logical channelwith lower PPPR than the PPPRs of the sidelink logical channels whichbelong to any LCG belonging to the same ProSe Destination and for whichdata is already available for transmission and lower than (and/or equalto) configured PPPR threshold.

The network may configure the above reliability threshold (e.g., PPPRthreshold) and/or priority threshold (e.g., PPPP threshold) forreporting of BSR via dedicated configuration.

As an example of implementations of the present disclosure, bufferstatus reporting (BSR) for sidelink communication may be performed asfollows. The sidelink buffer status reporting procedure is used toprovide the serving eNB with information about the amount of sidelinkdata available for transmission in the SL buffers associated with theMAC entity. In some implementations, the RRC controls BSR reporting forthe sidelink by configuring the two timers periodic-BSR-TimerSL andretx-BSR-TimerSL. Each sidelink logical channel belongs to a ProSeDestination. Each sidelink logical channel is allocated to an LCGdepending on the priority and optionally the PPPR of the sidelinklogical channel, and the mapping between LCG ID and priority andoptionally the mapping between LCG ID and PPPR which are provided byupper layers in logicalChGroupInfoList. the LCG is defined per ProSeDestination.

According to some implementations, a sidelink BSR shall be triggered ifany of the following events occur:

1> If the MAC entity has a configured SL-RNTI or a configured sidelinkV-RNTI (SL-V-RNTI), then:

2> SL data, for a sidelink logical channel of a ProSe Destination,becomes available for transmission in the RLC entity or in the PDCPentity and either the data belongs to a sidelink logical channel withhigher priority than the priorities of the sidelink logical channelswhich belong to any LCG belonging to the same ProSe Destination and forwhich data is already available for transmission, or there is currentlyno data available for transmission for any of the sidelink logicalchannels belonging to the same ProSe Destination, in which case theSidelink BSR is referred below to as “Regular Sidelink BSR”;

2> SL data, for a sidelink logical channel of a ProSe Destination,becomes available for transmission in the RLC entity or in the PDCPentity and either the data belongs to a sidelink logical channel withlower PPPR than the PPPRs of the sidelink logical channels which belongto any LCG belonging to the same ProSe Destination and for which data isalready available for transmission, or there is currently no dataavailable for transmission for any of the sidelink logical channelsbelonging to the same ProSe Destination;

2> SL data, for a sidelink logical channel of a ProSe Destination,becomes available for transmission in the RLC entity or in the PDCPentity and the data belongs to a sidelink logical channel with lowerPPPR than the PPPRs of the sidelink logical channels which belong to anyLCG belonging to the same ProSe Destination and for which data isalready available for transmission and lower than (and/or equal to)configured PPPR threshold;

2> UL resources are allocated and number of padding bits remaining aftera Padding BSR has been triggered is equal to or larger than the size ofthe Sidelink BSR MAC control element containing the buffer status for atleast one LCG of a ProSe Destination plus its subheader, in which casethe Sidelink BSR is referred below to as “Padding Sidelink BSR”;

2> retx-BSR-TimerSL expires and the MAC entity has data available fortransmission for any of the sidelink logical channels, in which case theSidelink BSR is referred below to as “Regular Sidelink BSR”;

2> periodic-BSR-TimerSL expires, in which case the Sidelink BSR isreferred below to as “Periodic Sidelink BSR”;

1> else:

2> An SL-RNTI or an SL-V-RNTI is configured by upper layers and SL datais available for transmission in the RLC entity or in the PDCP entity,in which case the Sidelink BSR is referred below to as “Regular SidelinkBSR”.

For Regular and Periodic Sidelink BSR:

1> if the number of bits in the UL grant is equal to or larger than thesize of a Sidelink BSR containing buffer status for all LCGs having dataavailable for transmission plus its subheader, then:

2> report Sidelink BSR containing buffer status for all LCGs having dataavailable for transmission;

1> else report Truncated Sidelink BSR containing buffer status for asmany LCGs having data available for transmission as possible, taking thenumber of bits in the UL grant into consideration.

For Padding Sidelink BSR:

1> if the number of padding bits remaining after a Padding BSR has beentriggered is equal to or larger than the size of a Sidelink BSRcontaining buffer status for all LCGs having data available fortransmission plus its subheader, then:

2> report Sidelink BSR containing buffer status for all LCGs having dataavailable for transmission;

1> else report Truncated Sidelink BSR containing buffer status for asmany LCGs having data available for transmission as possible, taking thenumber of bits in the UL grant into consideration.

If the Buffer Status reporting procedure determines that at least oneSidelink BSR has been triggered and not cancelled, then:

1> if the MAC entity has UL resources allocated for new transmission forthis TTI and the allocated UL resources can accommodate a Sidelink BSRMAC control element plus its subheader as a result of logical channelprioritization, then:

2> instruct the Multiplexing and Assembly procedure to generate theSidelink BSR MAC control element(s);

2> start or restart periodic-BSR-TimerSL except when all the generatedSidelink BSRs are Truncated Sidelink BSRs;

2> start or restart retx-BSR-TimerSL;

1> else if a Regular Sidelink BSR has been triggered, then:

2> if an uplink grant is not configured, then:

3> a Scheduling Request shall be triggered.

A MAC PDU shall, in some implementations, contain at most one SidelinkBSR MAC control element, even when multiple events trigger a SidelinkBSR by the time a Sidelink BSR can be transmitted in which case theRegular Sidelink BSR and the Periodic Sidelink BSR shall have precedenceover the padding Sidelink BSR.

In some implementations, the MAC entity shall restart retx-BSR-TimerSLupon reception of an SL grant.

All triggered regular Sidelink BSRs shall be cancelled in case theremaining configured SL grant(s) valid for this SC Period canaccommodate all pending data available for transmission in sidelinkcommunication or in case the remaining configured SL grant(s) valid canaccommodate all pending data available for transmission in V2X sidelinkcommunication. All triggered Sidelink BSRs shall be cancelled in casethe MAC entity has no data available for transmission for any of thesidelink logical channels. All triggered Sidelink BSRs shall becancelled when a Sidelink BSR (except for Truncated Sidelink BSR) isincluded in a MAC PDU for transmission. All triggered Sidelink BSRsshall be cancelled, and retx-BSR-TimerSL and periodic-BSR-TimerSL shallbe stopped, when upper layers configure autonomous resource selection.

In some implementations, the MAC entity shall transmit at most oneRegular/Periodic Sidelink BSR in a TTI. If the MAC entity is requestedto transmit multiple MAC PDUs in a TTI, then it may include a paddingSidelink BSR in any of the MAC PDUs which do not contain aRegular/Periodic Sidelink BSR.

All Sidelink BSRs transmitted in a TTI, according to someimplementations, always reflect the buffer status after all MAC PDUshave been built for this TTI. Each LCG shall report at the most onebuffer status value per TTI and this value shall be reported in allSidelink BSRs reporting buffer status for this LCG.

A Padding Sidelink BSR is not allowed to cancel a triggeredRegular/Periodic Sidelink BSR. A Padding Sidelink BSR is triggered for aspecific MAC PDU only and the trigger is cancelled when this MAC PDU hasbeen built.

The MAC header for SL-SCH according to an implementation of the presentdisclosure is as follows. The MAC header is of variable size andconsists of the following fields:

-   -   V: The MAC PDU format version number field indicates which        version of the SL-SCH subheader is used. Three format versions        are defined, and this field shall therefore be set to “0001”,        “0010”, and “0011”. If the DST field is 24 bits this field shall        be set to “0011”. The V field size is 4 bits;    -   SRC: The Source Layer-2 ID field carries the identity of the        source. It is set to the ProSe UE ID. The SRC field size is 24        bits;    -   DST: The DST field can be 16 bits or 24 bits. If it is 16 bits,        it carries the 16 most significant bits of the Destination        Layer-2 ID. If it is 24 bits, it is set to the Destination        Layer-2 ID. For sidelink communication, the Destination Layer-2        ID is set to the ProSe Layer-2 Group ID or Prose UE ID. For V2X        sidelink communication, the Destination Layer-2 ID is set to the        identifier provided by upper layers. If the V field is set to        “0001”, this identifier is a groupcast identifier. If the V        field is set to “0010”, this identifier is a unicast identifier;    -   LCD: The logical channel ID field uniquely identifies the        logical channel instance within the scope of one Source Layer-2        ID and Destination Layer-2 ID pair of the corresponding MAC SDU        or padding as described in Table 1 below. There is one LCID        field for each MAC SDU or padding included in the MAC PDU. In        addition to that, one or two additional LCID fields are included        in the MAC PDU, when single-byte or two-byte padding is required        but cannot be achieved by padding at the end of the MAC PDU. The        values of LCID from ‘01011’ to ‘10100’ identify the logical        channels used to send duplicated MAC SDUs from logical channels        of which the values of LCID from ‘00001’ to ‘01010’ respectively        in sequential order. The LCID field size is 5 bits;

TABLE 1 Index LCID values 00000 Reserved 00001-01010 Identity of thelogical channel 01011-10100 Identity of the logical channel which isused for duplication 10101-11011 Reserved 11100 PC5-S messages that arenot protected 11101 PC5-S messages ″Direct Security Mode Command″ and″Direct Security Mode Complete″ 11110 Other PC5-S messages that areprotected 11111 Padding

-   -   L: The Length field indicates the length of the corresponding        MAC SDU in bytes. There is one L field per MAC PDU subheader        except for the last subheader. The size of the L field is        indicated by the F field;    -   F: The Format field indicates the size of the Length field as        indicated in Table 2 below. There is one F field per MAC PDU        subheader except for the last subheader. The size of the F field        is 1 bit. If the size of the MAC SDU is less than 128 bytes,        then the value of the F field is set to 0, otherwise it is set        to 1;

TABLE 2 Index Size of Length field (in bits) 0 7 1 15

-   -   E: The Extension field is a flag indicating if more fields are        present in the MAC header or not. The E field is set to “1” to        indicate another set of at least R/R/E/LCID fields. The E field        is set to “0” to indicate that either a MAC SDU or padding        starts at the next byte;    -   R: Reserved bit, set to “0”.

The MAC header and subheaders are octet aligned.

FIG. 6 shows an example of a UE according to some implementations of thepresent disclosure. The examples of the present disclosure describedabove for UE side may be applied to this implementation. Specifically,this implementation may implement the implementation 1 described above.

A UE 600 includes at least one processor such as processor 610, at leastone memory such as memory 620 and a transceiver 630. The processor 610may be configured to implement proposed functions, procedures and/ormethods described in this description. Layers of the radio interfaceprotocol may be implemented in the processor 610.

Specifically, the processor 610 is configured to select to create aconfigured sidelink grant corresponding to transmissions of multiple MACPDUs. When data is available in a STCH associated with one or multiplecarriers and there is no configured sidelink grant on any carrier, amongthe one or multiple carriers, allowed for the STCH, the processor 610 isconfigured to trigger TX carrier (re-)selection procedure.

The processor 610 may include a MAC entity. The MAC entity may beconfigured by an upper layer to transmit using pools of resources in theone or multiple carriers based on sensing, or partial sensing, or randomselection. The upper layer may be RRC layer of the UE.

That the data is available in the STCH associated with the one ormultiple carriers and there is no configured sidelink grant on anycarrier allowed for the STCH may indicate that the data is available inthe STCH not associated with currently selected carrier among the one ormultiple carriers. The association between the STCH and the one ormultiple carriers may be configured by a network and/or pre-configured.The STCH may be allowed to be transmitted in at least one carrier amongthe one or multiple carriers based on CBR and/or PPPP of the STCH.

The memory 620 is operatively coupled with the processor 610 and storesa variety of information to operate the processor 610. The transceiver630 is operatively coupled with the processor 610, and transmits and/orreceives a radio signal.

The processor 610 may include application-specific integrated circuit(ASIC), other chipset, logic circuit and/or data processing device. Thememory 620 may include read-only memory (ROM), random access memory(RAM), flash memory, memory card, storage medium and/or other storagedevice. The transceiver 630 may include baseband circuitry to processradio frequency signals. When the implementations are implemented insoftware, the techniques described herein can be implemented withmodules (e.g., procedures, functions, and so on) that perform thefunctions described herein. The modules can be stored in the memory 620and executed by the processor 610. The memory 620 can be implementedwithin the processor 610 or external to the processor 610 in which casethose can be communicatively coupled to the processor 610 via varioustechniques as is known in the art.

According to implementation of the present disclosure shown in FIG. 6,the new triggering condition TX carrier (re-)selection can be added.More specifically, even if upper layer configures multiple carriers fora first V2X service and MAC entity selects a carrier among the multiplecarriers, and when new data for a second V2X service is available in alogical channel which is not associated with currently selected carrier,the TX carrier (re-)selection can be triggered, and a new carrier forthe second V2X service can be selected.

FIG. 7 shows an example of further details of a UE according to someimplementations of the present disclosure. The examples of the presentdisclosure described above for UE side may be applied to thisimplementation. Specifically, this implementation may implement theimplementation 1 described above.

A UE includes at least one processor such as a processor 610, a powermanagement module 611, a battery 612, a display 613, a keypad 614, asubscriber identification module (SIM) card 615, at least one memorysuch as a memory 620, at least one transceiver such as a transceiver630, one or more antennas 631, a speaker 640, and a microphone 641.

The processor 610 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 610. Theprocessor 610 may include ASIC, other chipset, logic circuit and/or dataprocessing device. The processor 610 may be an application processor(AP). The processor 610 may include at least one of a digital signalprocessor (DSP), a central processing unit (CPU), a graphics processingunit (GPU), a modem (modulator and demodulator). An example of theprocessor 610 may be found in SNAPDRAGON™ series of processors made byQualcomm®, EXYNOS™ series of processors made by Samsung®, A series ofprocessors made by Apple®, HELIO™ series of processors made byMediaTek®, ATOM™ series of processors made by Intel® or a correspondingnext generation processor.

The processor 610 is configured to select to create a configuredsidelink grant corresponding to transmissions of multiple MAC PDUs. Whendata is available in a STCH associated with one or multiple carriers andthere is no configured sidelink grant on any carrier, among the one ormultiple carriers, allowed for the STCH, the processor 610 is configuredto trigger TX carrier (re-)selection procedure.

The processor 610 may include a MAC entity. The MAC entity may beconfigured by an upper layer to transmit using pools of resources in theone or multiple carriers based on sensing, or partial sensing, or randomselection. The upper layer may be RRC layer of the UE.

That the data is available in the STCH associated with the one ormultiple carriers and there is no configured sidelink grant on anycarrier allowed for the STCH may indicate that the data is available inthe STCH not associated with currently selected carrier among the one ormultiple carriers. The association between the STCH and the one ormultiple carriers may be configured by a network and/or pre-configured.The STCH may be allowed to be transmitted in at least one carrier amongthe one or multiple carriers based on CBR and/or PPPP of the STCH.

The power management module 611 manages power for the processor 610and/or the transceiver 630. The battery 612 supplies power to the powermanagement module 611. The display 613 outputs results processed by theprocessor 610. The keypad 614 receives inputs to be used by theprocessor 610. The keypad 614 may be shown on the display 613. The SIMcard 615 is an integrated circuit that is intended to securely store theinternational mobile subscriber identity (IMSI) number and its relatedkey, which are used to identify and authenticate subscribers on mobiletelephony devices (such as mobile phones and computers). It is alsopossible to store contact information on many SIM cards.

The memory 620 is operatively coupled with the processor 610 and storesa variety of information to operate the processor 610. The memory 620may include ROM, RAM, flash memory, memory card, storage medium and/orother storage device. When the implementations are implemented insoftware, the techniques described herein can be implemented withmodules (e.g., procedures, functions, and so on) that perform thefunctions described herein. The modules can be stored in the memory 620and executed by the processor 610. The memory 620 can be implementedwithin the processor 610 or external to the processor 610 in which casethose can be communicatively coupled to the processor 610 via varioustechniques as is known in the art.

The transceiver 630 is operatively coupled with the processor 610, andtransmits and/or receives a radio signal. The transceiver 630 includes atransmitter and a receiver. The transceiver 630 may include basebandcircuitry to process radio frequency signals. The transceiver 630controls the one or more antennas 631 to transmit and/or receive a radiosignal.

The speaker 640 outputs sound-related results processed by the processor610. The microphone 641 receives sound-related inputs to be used by theprocessor 610.

According to implementation of the present disclosure shown in FIG. 7,the new triggering condition TX carrier (re-)selection can be added.More specifically, even if upper layer configures multiple carriers fora first V2X service and MAC entity selects a carrier among the multiplecarriers, and when new data for a second V2X service is available in alogical channel which is not associated with currently selected carrier,the TX carrier (re-)selection can be triggered, and a new carrier forthe second V2X service can be selected.

FIG. 8 shows an example of a network node according to implementationsof the present disclosure. The present disclosure described above fornetwork side may be applied to this implementation.

A network node 800 includes at least one processor such as processor810, at least one memory such as memory 820 and a transceiver 830. Theprocessor 810 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 810. Thememory 820 is operatively coupled with the processor 810 and stores avariety of information to operate the processor 810. The transceiver 830is operatively coupled with the processor 810, and transmits and/orreceives a radio signal.

The processor 810 may include ASIC, other chipset, logic circuit and/ordata processing device. The memory 820 may include ROM, RAM, flashmemory, memory card, storage medium and/or other storage device. Thetransceiver 830 may include baseband circuitry to process radiofrequency signals. When the implementations are implemented in software,the techniques described herein can be implemented with modules (e.g.,procedures, functions, and so on) that perform the functions describedherein. The modules can be stored in the memory 820 and executed by theprocessor 810. The memory 820 can be implemented within the processor810 or external to the processor 810 in which case those can becommunicatively coupled to the processor 810 via various techniques asis known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope of the present disclosure.

What is claimed is:
 1. A method performed by a wireless device operatingin a wireless communication system, the method comprising: determiningthat at least one currently selected carrier is not allowed to be usedfor a sidelink logical channel where data is available, wherein thesidelink logical channel is associated with a carrier; determining thata channel busy ratio (CBR) of the carrier is below a CBR thresholdassociated with a priority of the sidelink logical channel; consideringthe carrier as a candidate carrier for a transmission (TX) carrierselection or reselection based on i) the determination that the at leastone currently selected carrier is not allowed to be used for thesidelink logical channel where the data is available, and ii) thedetermination that the CBR of the carrier is below the CBR thresholdassociated with the priority of the sidelink logical channel; andselecting one or more carriers among candidate carriers for the TXcarrier selection or reselection including the carrier, wherein the CBRof the carrier comprises: a CBR value measured by the wireless devicebased on a CBR measurement result being available for the carrier; and avalue configured by a network for the carrier based on the CBRmeasurement result not being available for the carrier.
 2. The method ofclaim 1, wherein the method is performed by a media access control (MAC)entity of the wireless device.
 3. The method of claim 2, wherein the MACentity of the wireless device is configured by an upper layer of thewireless device to transmit using pools of resources in the carrierbased on sensing, partial sensing, or random selection.
 4. The method ofclaim 3, wherein the upper layer of the wireless device is a radioresource control (RRC) layer of the wireless device.
 5. The method ofclaim 1, wherein the data available in the sidelink logical channel isnot associated with the at least one currently selected carrier.
 6. Themethod of claim 1, wherein an association between the sidelink logicalchannel and the carrier is configured by at least one of a network or apre-configuration.
 7. The method of claim 6, wherein the data in thesidelink logical channel is allowed to be transmitted through thecarrier based on at least one of the CBR or a proximity-based services(ProSe) per-packet priority (PPPP) of the sidelink logical channel. 8.The method of claim 1, further comprising: transmitting the data in thesidelink logical channel through the carrier after the TX carrierselection or reselection.
 9. A wireless device configured to operate ina wireless communication system, the wireless device comprising: atransceiver; at least one memory; and at least one processor operablyconnectable to the at least one memory and storing instructions that,when executed by the at least one processor, perform operationscomprising: determining that at least one currently selected carrier isnot allowed to be used for a sidelink logical channel where data isavailable, wherein the sidelink logical channel is associated with acarrier; determining that a channel busy ratio (CBR) of the carrier isbelow a CBR threshold associated with a priority of the sidelink logicalchannel; considering the carrier as a candidate carrier for atransmission (TX) carrier selection or reselection based on i) thedetermination that the at least one currently selected carrier is notallowed to be used for the sidelink logical channel where the data isavailable, and ii) the determination that the CBR of the carrier isbelow the CBR threshold associated with the priority of the sidelinklogical channel; and selecting one or more carriers among candidatecarriers for the TX carrier selection or reselection including thecarrier, wherein the CBR of the carrier comprises: a CBR value measuredby the wireless device based on a CBR measurement result being availablefor the carrier; and a value configured by a network for the carrierbased on the CBR measurement result not being available for the carrier.10. The wireless device of claim 9, wherein the operations are performedby a media access control (MAC) entity of the wireless device.
 11. Thewireless device of claim 10, wherein the MAC entity of the wirelessdevice is configured by an upper layer of the wireless device totransmit using pools of resources in the carrier based on sensing,partial sensing, or random selection.
 12. The wireless device of claim11, wherein the upper layer of the wireless device is a radio resourcecontrol (RRC) layer of the wireless device.
 13. The wireless device ofclaim 9, wherein the data available in the sidelink logical channel isnot associated with the at least one currently selected carrier.
 14. Thewireless device of claim 9, wherein an association between the sidelinklogical channel and the carrier is configured by at least one of anetwork or a pre-configuration.
 15. The wireless device of claim 14,wherein the data in the sidelink logical channel is allowed to betransmitted through the carrier based on at least one of the CBR or aproximity-based services (ProSe) per-packet priority (PPPP) of thesidelink logical channel.
 16. The wireless device of claim 9, whereinthe operations further comprise: transmitting the data in the sidelinklogical channel through the carrier after the TX carrier selection orreselection.
 17. An apparatus comprising: at least one memory; and atleast one processor operably connectable to the at least one memory andstoring instructions that, when executed by the at least one processor,perform operations comprising: determining that at least one currentlyselected carrier is not allowed to be used for a sidelink logicalchannel where data is available, wherein the sidelink logical channel isassociated with a carrier; determining that a channel busy ratio (CBR)of the carrier is below a CBR threshold associated with a priority ofthe sidelink logical channel; considering the carrier as a candidatecarrier for a transmission (TX) carrier selection or reselection basedon i) the determination that the at least one currently selected carrieris not allowed to be used for the sidelink logical channel where thedata is available, and ii) the determination that the CBR of the carrieris below the CBR threshold associated with the priority of the sidelinklogical channel; and selecting one or more carriers among candidatecarriers for the TX carrier selection or reselection including thecarrier, wherein the CBR of the carrier comprises: a CBR value measuredby the wireless device based on a CBR measurement result being availablefor the carrier; and a value configured by a network for the carrierbased on the CBR measurement result not being available for the carrier.